Viscometer

ABSTRACT

A viscometer, particularly suited for blood viscometry. The inventive viscometer is circularly symmetrical and comprises a cylindrical channel for housing an unknown fluid and a ringshaped channel, concentric with the cylindrical channel, for housing a known Newtonian fluid. A floatable cover element is provided with a cylindrical projection adapted to associate with the cylindrical channel and the fluid housed therein, and is further provided with a ring-shaped projection adapted to associate with the ring-shaped channel and the Newtonian fluid housed therein. The cover element floats in the known Newtonian fluid with a fluid bearing action, the ring-shaped projection being coated with a material which is non-wettable, and the channel being coated with a material wettable by the known fluid. The block in which is defined the cylindrical channel and the block in which is defined the ring-shaped channel are rotated in opposite directions, and the relative velocity of rotation therebetween is adjusted until the floating cover element is stationary. The relative rotation between the cylindrical channel block and the ring-shaped channel block is proportional to the viscosity of the unknown sample.

United States Patent Kaufman et al.

[451 June 6, 1972 [54] VISCOMETER Primary ExaminerL0uis R. Prince [72]Inventors: William M. Kaufman, Chevy Chase; ji g g: i gg wbRoskos HarryP. Kling, Glenarm, both of Md. omeye] e ace Son [73] Assignee: HittmanAssociates, Inc., Columbia, Md. ABSTRACT [22] Fil d; A 21, 1970 Aviscometer, particularly suited for blood viscometry. The inventiveviscometer is circularly symmetrical and comprises a [2]] Appl' 30,566cylindrical channel for housing an unknown fluid and a ringshapedchannel, concentric with the cylindrical channel, for [52] US. Cl..73/59 housing a known Newtonian fluid- A floatable cover element [5 1]1m. CL 01 "/10 is provided with a cylindrical projection adapted toassociate [53] n w f Search" mun/59 60 with the cylindrical channel andthe fluid housed therein, and is further provided with a ring-shapedprojection adapted to [56] References Cited associate with thering-shaped channel and the Newtonian fluid housed therein. The coverelement floats in the known UNITED STATES PATENTS Newtonian fluid with afluid bearing action, the ring-shaped projection being coated with amaterial which is non-wettable, Gulliksen ..73/59 and the Channel beingcoated with a material wenable y the 3'O79787 3/1963 known fluid. Theblock in which is defined the cylindrical channel and the block in whichis defined the ring-shaped 3 545 257 12/1970- channel are rotated inopposite directions, and, the relative FOREIGN PATENTS OR APPLICATONSvelocity of rotation therebetween is adjusted until the floating coverelement is stationary. The relative rotation between the 926,094 4/1955Germany ..73/60 cyfindfica] channel block and the ring-shaped channel bIk is I proportional to the viscosity of the unknown sample.

12 Claims, 1 Drawing Figure 3a 28 I I uni '1 J 'J. "P I 5 1! MWVISCOMETER BACKGROUND OF THE INVENTION There are many viscometers knownto the prior art. However, each of these known viscometers suffers fromat least one of a large number of drawbacks. For example, someviscometers, such as the Ostwald viscometer, do not apply a uniform rateof shear to the sample andare not very useful at low shear rates. Othercommercially available viscometers are either not sufficiently sensitiveor are extremely delicate and expensive.

Particularly in the field of blood viscometry, it is important that theviscometer function witha small fluid sample-the patients in need ofblood viscometry work often have already suffered a considerable loss ofblood. A major drawback of several known viscometers is that a largeblood sample is required for an accurate determination of viscosity.

Another typical disadvantage which plagues the field of viscometry isthat many of the known viscometers are so complex that skilledtechnicians are needed for their operation and for an accurateevaluation of their results. 1

A further disadvantage associated with most known viscometers is thatsolid bearing surfaces are required between the moving parts and thefluid or fluids. These bearing surfaces become worn, and because theviscometers deal with precise measurements at low shear rates, the wornbearing surfaces may introduce large errors in the viscositymeasurements.

" It is toward the elimination of the above-mentioned draw- .backs inthe art of viscometry that the present invention is directed.

SUMMARY OF THE INVENTION The present invention relates to a viscometer,particularly suited to blood viscometry, which is relatively free fromthe disadvantages plaguing the viscometers of the prior art. Theinventive viscometer is capable of yielding viscosity measurements withsmall fluid samples, on the order of l to 2 milliliters, and withinapproximately 1 minute; it may be operated by personnel with limitedscientific training; it is simple in construction and is yet rugged; itis inexpensive to manufacture, and yet maintains accurate readings atlow shear rates; and it may be quickly and easily cleaned and readiedfor subsequent operations.

A major advantage of the inventive viscometer, responsible for many ofthe desirable features noted above, is that contiguous solid bearingsurfaces between the driven members and the torque sensing member of thepresent viscometer are totally absent. In this manner, one very criticalsource of static frictional forces is substantially eliminated. Moreparticularly, rather than applying solid bearing surfaces between thedriven members and the torque sensing member, the inventive viscometermakes use of fluid bearings.

lt is true that solid bearing surfaces are present in the viscometer ofthe present invention. However, these bearing surfaces are directlycoupled to motors which can be given enough torque to overcome thestatic frictional forces. It is between the driven members and thesensing member that the static frictional forces are most critical; andhere, no solid bearing surfaces are present.

In construction, the viscometer of the present invention is extremelysimple. It comprises, basically, three circularly concentricelements-one passive element and a pair of driven elements. If desired,the number of passive elements may be increased to two, thus simplifyingthe charging and cleansing operations. A readout mechanism is alsoprovided.-

The three basic elements of the inventive viscometer are rotatablerelative to one another. These elements are interconnected by means of aNewtonian fluid having known properties, and an unknown sample of fluid.One of the three movable elements, housing the unknown fluid sample, isrotated at a fixed rate of rotation and in a first sense. Another of therotatable elements, housing the known fluid, is rotated in a second andopposite sense and at a variable speed which is adjusted so that thethird element comes to a standstill. The viscosity of the unknown fluidis proportional to the speed of rotation of the second rotatable elementwhich is necessary to bring the third element to a standstill.

Accordingly, it is the main object of the present invention to provide aviscometer, particularly suitable for blood viscometry, which is simplein design, inexpensive to manufacture, which may be used by unskilledtechnicians and which accurately provides viscosity measurements at lowshear rates.

Another object of the present invention is to provide a viscometer whichis capable of yielding viscosity measurements without requiring largefluid samples. 7

An additional object of the present invention is to provide a viscometerwhich is rugged and which can, therefore, withstand rough handlingduring shipment, relocation and continued use.

It is yet a further object of the invention to provide a novelviscometer having no contiguous solid bearing surfaces between drivenelements and the passive torque sensing element, thereby eliminating acritical source of difficulties, particularly at low shear rates,arising from static frictional forces.

These and other objects of the invention,'as well as many of theattendant advantages thereof, will become more readily apparent whenreference is made to the following description taken in conjunction withthe accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING The sole FIGURE is a cross-sectionthrough the viscometer of the present invention.

DETAILED DESCRIPTION OF THE DRAWING block 14 is centered at thecenterline l2 and has provided Y therein a shallow bore 16 atthe-uppermost region thereof. Concentric with the cylindrical block 14is a ring-shaped driven block 18 having therein a ring-shaped trough 20.The bore 16 defines a chamber which is adapted to house an unknown fluidsample 22 of relatively high viscosity; and the trough 20 defines achamber which is adapted to house a known Newtonian fluid 24 ofrelatively low viscosity. If the unknown fluid is of a relatively lowviscosity compared to the known Newtonian fluid, it is contemplated,butnot essential, that the unknown be housed in the trough 20 while theknown Newtonian fluid would be housed in the chamber defined by the bore16.

A passive torque sensing cover plate, indicated generally at 25, iscoextensive with block 14 and block 18, and is shown to include a firstdisc-like member 26 having a ring-shaped protrusion 28 integraltherewith and a second disc-like member 30 having a cylindricalprotrusion 32 integral therewith.

As seen from the FIGURE, the ring-shaped protrusion 28 is shaped anddimensioned so as to comfortably fit within the chamber 20, and so thatit may float in the known Newtonian fluid 24. Similarly, the cylindricalprotrusion 32 is shaped and dimensioned so that when the cover plate 25floats in the known fluid 24, the surface of the cylindrical protrusion32 smoothly rides in the unknown fluid 22. It should be noted that thecylindrical protrusion 32 is shaped, at its lowermost region 33, as acone. Also, it should be noted that the surface of the known fluid 22 isat the same level as the widest portion of the conical region 33. Inthis manner, the maximum efficiency of the device is realized. As analternative configuration, the base of the chamber 16 could be madeconically convex while the bottom of protrusion 32 could be made planar.

When the viscometer 10 operates, the cover plate 25 floats, through theaction of the ring-shaped projection 28, in the Newtonian fluid 24. Thebearing between the protrusion 28 and the block 18 is thus a pure fluidbearing. This fluid bearing The surface of the inner surface of channel20 is coated with a material wettable by the known fluid. For example,with the known fluid being water, the inner surface of channel 20 couldbe coated with a glass. By so coating protrusion 28 and the innersurface of channel 20, surface tension forces will be set up which causethe floating part to be maintained out of contact with all adjacentsolid surfaces. This ensures a fluid bearing even at zero relativemotion and thereby ensures reduced stiction," i.e., cover'plate 25 isable to rotate without having to overcome a high level of torque.

I To facilitate the changing of theunknown fluid sample 22 and thecleansing of the chamber 16, the cover plate 25 is divided into firstand second disc-like members 26 and 30, respectively. The disc-likemember 26 has, therethrough, a centrally located bore 34, which bore isadapted to support the disc-like member 30. For this reason, the unitingsurface 35, between the members 26 and 30, is stepped.

As is explained below, when the viscometer operates, integrity must bemaintained between the respective disc-like members 26 and 30.Therefore, member 30 is provided with a plurality of projections 36adapted to mate with corresponding indentations in the member 26. Thus,relative movement between members 26 and 30 is prevented.

The cover plate 25, as explained above, is divided into the separatemembers 26 and 30, respectively, only for reasons of convenience. Whenit is desired to change the unknown sample 22 housed in the cylindricalchamber 16, the disc-like member 30 is lifted awayfrom the disc-likemember 26, ready access then being provided to the chamber 16. When thechamber 16 is cleansed and a new sample is inserted, the member 30 isreplaced. Of course, if this convenience is not desired, members 26 and30 may be made integral. I

In preparing the viscometer of the present invention for aviscosityreading, the procedure is as follows. First, a fixed quantityof unknown fluid is introduced into the cylindrical bore 16. The fixedquantity is measured to moderate accuracy by, for example, a pipette. Atthis time, the known Newtonian fluid 24 is housed in the ring-shapedtrough 20. Then, the disclike member 30 is positioned in its housingprovided in the disc-like member 26. It is suggested at this time thatthe leveling of the viscometer 25 be checked.

To ensure that the base 48 of the viscometer assembly is level,adjusting screws 37 are provided. While any number of adjustment screws37 may be fitted to the case 66 of the viscometer, three adjustingscrews are suggested. A bubble chamber 38, for example, may bepositioned on the base 48, thereby serving as a check to ensure that thebase is properly leveled.

Once the leveling of the viscometer assembly 25 is completed, the nextstep is to adjust, with accuracy, the level at which the projection 32rides in the unknown fluid sample 22. It is desirable that theprojection 32 ride so that the apex of the conical region 33 is near,but yet is not touching the base of the chamber 16.

The level of the member 32 is adjusted by acting on the height of theknown fluid housed in the ring-shaped trough 20.

. For this purpose. an opening is fitted in the block 18 and isindicated at 39. A support member 40 is appended to the block 18 andassociates with the opening 39 and with a bellows found that by socontrolling the wetting characteristics of these surfaces, surfacetension forces are most advantageously used and efficiently maintain theprotrusion 28 out of contact with the trough and thereby maintain thecylindrical projection 32 out of contact with the bore 16. In thismanner, and as noted above, one critical source of static friction iseliminated, thus ensuring accurate measurements at low shear rates.

With reference again to the FIGURE, the rotatable relationship betweenthe blocks 14 and 18 and thecover plate will be explained. Thecylindrical blockv 14 is rotatably mounted on a base 48 by means of aball bearing assembly 50; and the ring-shaped block 18 is mounted on thebase 48 by means of a ball bearing assembly 52.

A motor 54 of constant speed is supported on the base and is associatedwith the cylindrical block 14 through a drive shaft 56, this motor beingadapted to rotate in a first sense, for example, clockwise. A secondmotor 58, of variable speed, is also mounted on the base 48 and servesto drive the block 18. On the output shaft 60 of the variable speedmotor 58 is a vertically mounted disc 62, as of rubber, which disc bearsagainst the inner surface of the ring-shaped block 18. Thus, when themotor 58 is operative, block 18 rotates. The motor 58 is adapted torotate block 18 in a sense opposite from the sense of rotation of theblock 14 which is rotated by the motor 54; in

' this example, the variable speed motor 58 is adapted torotate theblock 18 in a counterclockwise sense.

The variable speed motor 58 is provided to allow the relative speedsbetween the two moving fluid chambers to be adjusted so that thefloating member is absolutely still. The result of such adjustment isthat the viscosity of the unknown fluid may be readily determined. Whenthe floating member is stationary, the viscosity of the unknown fluid isdirectly proportional to the speed of the block 18 and thus the variablespeed sure that there is no relative motion between the base 48 and thefloating member 25. In the drawing, themeans used for ensuring that thedisc-like member 26 is stationary with respect to the base 48 takes theform of a wire, or hairline 63 rigidly attached to the base 48 and agrid-like arrangement carved directly onto the disc-like member 26, thegrid arrangement being shown at 64. Alternatively, other well-knowntechniques of motion sensing may be employed, such as interferometry,capacitance sensing or inductance sensing, naming just a few examples.

Associated with the variable speed motor 58 is a meter 70, which may be,for example, a tachometer. As noted previously, and as will be morefully explained below, the viscometer 10 of the present inventiondepends upon the principle that the speed of the block 18 isproportional to the viscosity of the unknown fluid 22 when the floatingmember is stationary.

I Therefore, by fitting the variable speed motor 58 with a meter 70capable of reading the motor speed, and thus the rotational speed ofblock 18, the viscosity of the fluid 22 may readily be determined. Infact, the meter 70 may be calibrated in such a manner that its readingis a direct indication of the viscosity of the unknown fluid.Alternatively, since the speed of the motor 58 is an indication of theviscosity of the fluid 22, the position of the speed control knobassociated with this motor may be used to give a direct reading ofviscosity. That is, the speed control knob of the motor 58 may becalibrated in terms of viscosity.

As shown in the FIGURE, the operating elements of the viscometer 10 maybe shock mounted, as by means of springs 65, and may be housed in anenclosure defined by a base 66 and a removable and transparent cover 68.To best make use of the shock-absorbing springs, the total sprung massof the device and the spring constants of the springs 65 are chosen soas to constitute an efficient vibration damper for the random ambientvibrations likely to be found in the average clinical laboratory. Inthis manner, the ruggedness and the accuracy of the inventive viscometerare greatly enhanced. And, by enclosing the viscometer in a sealed case,the viscosity readings may be taken without the effects of the externalenvironment. Further, to ensure accurate functioning of the viscometer,notwithstanding changes in environmental temperatures, it iscontemplated that the internal temperature of the case be monitored andcontrolled in such a manner that the viscometer 25 experiences aconstant temperature under all ambient conditions.

The operation of the viscometer forming a part of the present inventionis as follows. The cover 68 is removed and the disc-like member 30 islifted from its seat in the disc-like member 26. A small charge of anunknown fluid, l to 2 milliliters, is placed in the cylindrical chamber16. Then, the member 30 is replaced so that the projections 36 associatewith the corresponding depressions in the member 26. The liquid level inthe ring-shaped trough is then altered, if necessary, by means of thebellows chamber 41 and the adjustment screw 43, so that the cover platefreely floats in the known Newtonian fluid 24 and so that thecylindrical projection 32 extends into the unknown fluid 22 withoutbearing on the bottom surface of the chamber 16. As noted above, the

ring-shaped projection 28 is coated with a material non-wetta-' ble bythe known fluid 24 and the surface of the channel 20 is coated with amaterial wettable by the known fluid. In this manner, and due to theeffects of surface tension forces, the cover plate 25 is maintainedsubstantially centered with respect to the center line 12.

With the cover 68 over the base 66, the constant speed motor is startedand is made to rotate at a speed of, for example, 0.10 rpm. This lowspeed ensures that inertial effects during the start-up time arenegligible. Then, the variable speed motor 58 is activated and isadjusted so that the cover plate 25 is precisely stationary.

Since the relative speed between the chambers 16 and 20 is a directindication of the viscosity of the unknown fluid 22, and since the motor54 is of constant speed, the speed of motor 58 could be made to yielddirect indications of viscosity. As explained above, this may be donewith the meter 70, calibrated to fluid viscosity or, alternatively, withthe reading on the control knob of the motor 58. This meter reading, inaccordance with the present invention, must be taken at a time when ithas been determined that the cover plate 25 is motionless.

The entire operation described above may be carried out in a matter ofseconds. This is particularly important since, when dealing with bloodviscosity, the operator is allowed a maximum of approximately 60 secondsbetween withdrawing a fresh blood sample and completing the viscositymeasurement. The problem of coagulation may become significant withdelays longer than 60 seconds.

As the motors 54 and 58 rotate the blocks 14 and 18 in oppositedirections, counteracting forces are applied to the cover plate 25 inthe form of shear forces in the two respective fluids 22 and 24. if thetorque-versus-speed relationship between the ring-shaped block 18 andthe disc-like member 26, associated with one another through the actionof the known Newtonian fluid 22, is known, and if the relationshipbetween the shear stress and rotation rate in the structure defined bythe cylindrical block 14 and the cylindrical protrusion 32 is known fromprevious calibrations, then a measurement of rotation rate in thering-like block 18 is a direct measurement of viscosity of the unknownsample of fluid at the selected rate of shear.

As noted previously, the only connection between the cover plate 25 andthe ring-shaped block 18 is in the form of a fluid bearing. This is ofparticular advantage especially in blood viscometry. In this technology,extremely low rotational velocities and extremely low torques areinvolved. With mechanical bearings, erratic frictional forces areintroduced, and hence, inaccuracies are introduced. Further, since theviscosity of the unknown fluid is detemiined by the condition that thecover plate 25 is absolutely motionless, mechanical bearings would tendto introduce harmful inaccuracies related to inertial forces. With purefluid bearings, on the other hand, these drawbacks are eliminated. Withpure fluid bearings, the frictional forces are constant. Further, theinertial forces which must be overcome in introducing relative motionbetween two bodies contacted only by a fluid bearing, are relativelysmall. Thus, with the present invention, extremely accurate viscosityreadings may be taken of an'unknown fluid, even when low shear rates areencountered.

Above, there. has been described a particular embodiment of the presentinvention. It should be understood, however, that this embodiment hasbeen described for purposes of illustration only. For example, thecone-plate structure of the chamber housing the unknown fluid may takemany other forms. Numerous drive mechanisms other than that describedherein may be employed. And, if desired, adjustment means may beprovided on the drive mechanism associated with the fixed speed motor,thus ensuring that the motor is properly matched to the shear rate ofthe unknown fluid. The instrument of the present invention may beadapted for continuous flow-through operation, and the instrument may bedeveloped for automatic operation, with a numerical readout. Stillfurther, the powering may be by means of standard household power or maybe by battery for portable operation. In short, many alterations may bemade without departing from the teachings of the present invention. Itis the intent, therefore, that this invention not be limited by theabove, but only as defined in the appended claims.

We claim: 1

1. A circularly symmetrical viscometer adapted for determining theviscosity of an unknown fluid by comparing the viscosity of said unknownfluid with the viscosity of a known fluid, the viscometer comprising: afirst circularly symmetrical chamber for housing a first fluid; a secondcircularly symmetrical chamber, concentric with said first circularlysymmetrical chamber, for housing a second fluid; a circularlysymmetrical structure adapted to associate with said first and saidsecond fluids, said structure being provided with afirst projectionshaped so as to comfortably fit within said first chamber and associatewith said first fluid, and further being provided with a secondprojection shaped so as to comfortably fit within said second chamber insuch a manner as to contact said second fluid, displace a certain amountthereof, and consequently float therein, said second projection beingcoated with a material non-wettable by said second fluid, and theinternal wall of said second chamber being coated with a materialwettable by said second fluid; means for rotating said first chamber ina first sense; means for rotating said second chamber in a second andopposite sense; and means for determining the relative rotationalvelocity between the floating structure and said fluid-carryingchambers, thereby providing for the determination of the viscosity ofsaid unknown fluid.

2. The viscometer as defined in claim 1, and further comprising meansfor adjusting the relative speed of rotation between said first and saidsecond chambers so that said floating structure is precisely stationary;and means for reading the viscosity of said unknown fluid sample whensaid floating structure is precisely stationary.

3. The viscometer as defined in claim 1, wherein said first fluid has ahigher viscosity than said second fluid.

4. The viscometer as described in claim 1, wherein said first circularlysymmetrical chamber and said first projection are cylindrical shaped;wherein said second circularly symmetrical chamber and said secondprojection are ring shaped; and wherein said first and second chambersand said first and second projections are concentric.

5. The viscometer as recited in claim 4, wherein said means for rotatingone of said chambers is a variable speed motor; wherein the means forrotating the other of said chambers is a fixed speed motor; and furthercomprising means associated with said variable speed motor for directlyreading the viscosity of said unknown fluid sample.

6. The viscometer as recited in claim 5, and further comprising meansfor adjusting the drive mechanism associated with said fixed speed motorin order to select the shear rate of the unknown fluid.

7. The viscometer as recited in claim 5, wherein said floating structurecomprises two distinct elements and wherein the removal of one of thetwo elements provides access to said first circularly symmetricalchamber.-

8. The viscometer as defined in claim 5, and further comprising meansfor adjusting the height of the second fluid in said second circularlysymmetrical chamber.

9. The viscometer as recited in claim 5, and further including means forshock mounting the elements of said viscome ter.

10. The viscometer as recited in claim 5, and further comprising covermeans for isolating the floating parts of the viscometer from theexternal environment.

11. The viscometer as recited in claim 5, and further comprising meansfor ensuring temperature stability for the temperature-sensitiveelements of the viscometer.

12. The viscometer as recited in claim I, wherein said means forrotating said first chamber operates at a constant velocity; whereinsaid means for rotating said second chamber operates at a variablevelocity; and further comprising means for determining said variablevelocity; and means for determining the velocity conditions cxistingwhen said floating structure is motionless.

* I It i

1. A circularly symmetrical viscometer adapted for determining theviscosity of an unknown fluid by comparing the viscosity of said unknownfluid with the viscosity of a known fluid, the viscometer comprising: afirst circularly symmetrical chamber for housing a first fluid; a secondcircularly symmetrical chamber, concentric with said first circularlysymmetrical chamber, for housing a second fluid; a circularlysymmetrical structure adapted to associate with said first and saidsecond fluids, said structure being provided with a first projectionshaped so as to comfortably fit within said first chamber and associatewith said first fluid, and further being provided with a secondprojection shaped so as to comfortably fit within said second chamber insuch a manner as to contact said second fluid, displace a certain amountthereof, and consequently float therein, said second projection beingcoated with a material non-wettable by said second fluid, and theinternal wall of said second chamber being coated with a materialwettable by said second fluid; means for rotating said first chamber ina first sense; means for rotating said second chamber in a second andopposite sense; and means for determining the relative rotationalvelocity between the floating structure and said fluid-carryingchambers, thereby providing for the determination of the viscosity ofsaid unknown fluid.
 2. The viscometer as defined in claim 1, and furthercomprising means for adjusting the relative speed of rotation betweensaid first and said second chambers so that said floating structure isprecisely stationary; and means for reading the viscosity of saidunknown fluid sample when said floating structure is preciselystationary.
 3. The viscometer as defined in claim 1, wherein said firstfluid has a higher viscosity than said second fluid.
 4. The viscometeras described in claim 1, wherein said first circularly symmetricalchamber and said first projection are cylindrical shaped; wherein saidsecond circularly symmetrical chamber and said second projection arering shaped; and wherein said first and second chambers and said firstand second projections are concentric.
 5. The viscometer as recited inclaim 4, wherein said means for rotating one of said chambers is avariable speed motor; wherein the means for rotating the other of saidchambers is a fixed speed motor; and further comprising means associatedwith said variable speed motor for directly reading the viscosity ofsaid unknown fluid sample.
 6. The viscometer as recited in claim 5, andfurther comprising means for adjusting the drive mechanism associatedwith said fixed speed motor in order to select the shear rate of theunknown fluid.
 7. The viscometer as recited in claim 5, wherein saidfloating structure comprises two distinct elements and wherein theremoval of one of the two elements provides access to said firstcircularly symmetrical chamber.
 8. The viscometer as defined in claim 5,and further comprising means for adjusting the height of the secondfluid in said second circularly symmetrical chamber.
 9. The viscometeras recited in claim 5, and further including means for shock mountingthe elements of said viscometer.
 10. The viscometer as recited in claim5, and further comprising cover means for isolating the floating partsof the viscometer from the external environment.
 11. The viscometer asrecited in claim 5, and further comprising means for ensuringtemperature stability for the temperature-sensitive elements of theviscometer.
 12. The viscometer as recited in claim 1, wherein said meansfor rotating said first chamber operates at a constant velocity; whereinsaid means for rotating said second chamber operates at a variablevelocity; and further comprising means for determining said variablevelocity; and means for determining the velocity conditions existingwhen said floating structure is motionless.